GOSSIP : a vertex detector combining a thin gas layer as signal generator with a CMOS readout pixel array Gas On Slimmed SIlicon Pixels

Time Projection Chamber (TPC): 2D/3D Drift Chamber The Ultimate Wire (drift) Chamber E-field (and B-field) Wire Plane + Readout Pads track of charged particle Wire plane Pad plane

Let us eliminate wires: wireless wire chambers 1996: F. Sauli: Gas Electron Multiplier (GEM)

1995 Giomataris & Charpak:MicroMegas Ideally: a preamp/shaper/discriminator channel below each hole….

The MediPix2 pixel CMOS chip 256 x 256 pixels pixel: 55 x 55 μm 2 per pixel:- preamp - shaper - 2 discr. - Thresh. DAQ - 14 bit counter - enable counting - stop counting - readout image frame - reset We apply the ‘naked’ MediPix2 chip without X-ray convertor!

MediPix2 pixel sensor Brass spacer block Printed circuit board Aluminum base plate Micromegas: V Cathode (drift) plane: V Baseplate Drift space: 15 mm (gas filled) Very strong E-field above (CMOS) MediPix! Cubic drift volume: 14 x 14 x 14 mm 3 cosmic muon

We always knew, but never saw: the conversion of 55 Fe quanta in Ar gas No source, 1s 55 Fe, 1s 55 Fe, 10s Friday 13 (!) Feb 2004: signals from a 55 Fe source (220 e- per photon); 300  m x 500  m clouds as expected 14 mm The Medipix CMOS chip faces an electric field of 350 V/50 μm = 7 kV/mm !!

Eff = e -Thr/G Thr: threshold setting (#e-) G: Gas amplification Prob(n) = 1/G. e -n/G no attachment homogeneous field in avalanche gap low gas gain simple exponential grown of avalanche  No Curran or Polya distributions but simply: Single electron efficiency

New trial: NIKHEF, March 30 – April 2, 2004 Essential: try to see single electrons from cosmic muons (MIPs) Pixel preamp threshold: 3000 e- (due to analog-digital X-talk) Required gain: 5000 – New Medipix New Micromegas Gas: He/Isobutane 80/20 !Gain up to 30 k! He/CF4 80/20 …… It Works!

He/Isobutane 80/20 Modified MediPix Sensitive area: 14 x 14 x 15 mm 3 Drift direction: Vertical max = 15 mm

He/Isobutane 80/20 Modified MediPix Sensitive area: 14 x 14 x 15 mm 3 Drift direction: Vertical max = 15 mm

He/Isobutane 80/20 Modified MediPix δ-ray? Sensitive area: 14 x 14 x 15 mm 3 Drift direction: Vertical max = 15 mm

MediPix modified by MESA+, Univ. of Twente, The Netherlands Pixel Pitch: 55 x 55 μm 2 Bump Bond pad: 25 μm octagonal 75 % surface: passivation Si 3 N 4 New Pixel Pad: 45 x 45 μm 2 Insulating surface was 75 % Reduced to 20 % Non ModifiedModified

Vernier, Moire, Nonius effect Pitch MediPix: 55 μm Pitch Micromegas: 60 μm Periodic variation in gain per 12 pixels Focussing on (small) anode pad Continues anode plane is NOT required Reduction of source capacity! Non-modified MediPix Modified MediPix has much less Moire effect No charge spread over 2 or 4 pixels

Modified Non Modified InGrid: perfect alignment of pixels and grid holes! Small pad: small capacitance! De-focussing focusing De-focussing

INtegrate Micromegas GRID and pixel sensor ‘Micromegas’ By ‘wafer post processing’ at MESA+, Univ. of Twente InGrid

Integrate GEM/Micromegas and pixel sensor: InGrid ‘GEM’ ‘Micromegas’ By ‘wafer post processing’

-For KABES II, there are two options. The TPC with transverse drift option would need strips rather than pixels. But it could be interesting to have an InGrid-like integrated mesh. The thin Si or CMOS+gas option would need a very high rate capability. -CAST (CERN Axion Solar Telescope) seems to be a more straightforward application. It simply requires a possibility of triggering a common stop. This is why Esther Ferrer-Ribas, from CAST, will join us. - The polarimetry application (challenging Belazzini) is very interesting for people from the Astrophysics division. The requirement is very similar to CAST's. - The MicroTPC might have applications in nuclear physics or in Babar, for instance. - There are other applications (X-ray beam monitor for SOLEIL) which I can talk about tomorrow. - The protection issue is essential in all Micromegas applications.

! With 1 mm layer of (Ar/Isobutane) gas we have a fast TPC! thick enough for 99 % MIP detection efficiency thin enough for max. drift time < 25 ns (LHC bunchX) Replace {Si sensor + amplifier} by gas layer:  tracker for intense radiation environment After all: until 1990 most vertex detectors were gas detectors! Si solved granularity problems associated with wires.

CMOS pixel array MIP Micromegas (InGrid) GOSSIP: Gas On Slimmed SIlicon Pixels Drift gap: 1 mm Max drift time: 16 ns MIP CMOS pixel chip Cathode foil

Essentials of GOSSIP: Generate charge signal in gas instead of Si (e-/ions versus e-/holes) Amplify # electrons in gas (electron avalanche versus FET preamps) Then: No radiation damage in depletion layer or pixel preamp FETs No power dissipation of preamps, required for Si charge signals No detector bias current 1 mm gas layer + 20 μm gain gap + CMOS (almost digital!) chip After all: it is a TPC with 1 mm drift length (parallax error!) Max. drift length: 1 mm Max. drift time: 16 ns Resolution: 0.1 mm  1.6 ns

Ageing Efficiency Position resolution Rate effects Radiation hardness HV breakdowns Power dissipation Material budget

Ageing Remember the MSGCs…… Little ageing: the ratio (anode surface)/(gas volume) is very high w.r.t. wire chambers little gas gain: 5 k for GOSSIP, 20 – 200 k for wire chambers homogeneous drift field + homogeneous multiplication field versus 1/R field of wire. Absence of high E-field close to a wire: no high electron energy; little production of chemical radicals Confirmed by measurements (Alfonsi, Colas) But: critical issue: ageing studies can not be much accelerated!

Efficiency Determined by gas layer thickness and gas mixture: Number of clusters per mm: 3 (Ar) – 10 (Isobutane) Number of electrons per cluster: 3 (Ar) - 15 (Isobutane) Probability to have min. 1 cluster in 1 mm Ar: 0.95 With nice gas: eff ~ 0.99 in 1 mm thick layer should be possible But……. Parallax error due to 1 mm thick layer, with 3 rd coordinate 0.1 mm: TPC/ max drift time 16 ns; σ = 0.1 mm; σ = 1.6 ns: feasible! Lorentz angle We want fast drifting ions (rate effect) little UV photon induced avalanches: good quenching gas

Position resolution Transversal coordinates limited by: Diffusion: single electron diffusion 0 – 40/70 µm weighed fit: ava 20/30 µm 10 e- per track: σ = 8/10 µm pixel dimensions: 20 x 20 – 50 x 50 μm 2 Note: we MUST have sq. pixels: no strips (pad capacity/noise) Good resolution in non-bending plane! Pixel number has NO cost consequence (m 2 Si counts) Pixel number has some effect on CMOS power dissipation δ-rays: can be recognised & eliminated 3 rd (drift) coordinate limited by: Pulse height fluctuation gas gain (5 k), pad capacity, # e- per cluster With Time Over Threshold: σ = 1 ns ~~ 0.1 mm 0Q0Q 20 ns

Rate effects time 0Q0Q 20 ns ~10 e- per track (average) gas gain 5 k most ions are discharged at grid after traveling time of 20 ns a few percent enter the drift space: 2 cm from beam pipe: 10 tracks cm ns MHz cm -2 ! Some ions crossing drift space: takes 20 – 200 μs! ion space charge has NO effect on gas gain ion charge may influence drift field, but this does little harm ion charge may influence drift direction: change in lorentz angle ~0.1 rad B-field should help

Data rate Hit Pixel (single electron) data: 8 bit column ID 8 bit row ID 4 bit timing leading edge 4 bit timing trailing edge total 24 bits/hit pixel 100 e-/ 25 ns cm 2  380 Gb/s per chip (2 x 2 cm 2 ) Cluster finding: reduction factor 10: 40 Gb/s Horisberger: Data rate, DAQ, data transmission is a limiting factor for SLHC Required: rad hard optical links with 1 mm 3 light emittors per chip!

Radiation hardness Gas is refreshed: no damage CMOS 130 nm technology:? TID ? NIEL ? SEU: design/test need only modest pixel input stage How is 40 Gb/s hit pixel data transferred? need rad hard optical link per chip!

HV breakdowns: InGrid issue 4) Protection Network 1) High-resistive layer 2) High-resistive layer 3) ‘massive’ pads

Power dissipation For GOSSIP CMOS Pixel chip: Per pixel: - input stage (1.8 μA/pixel) - monostable disc/gate Futher: data transfer logic guess: 0.1 W/cm 2  Gas Cooling feasible!

Detector Material budget ‘Slimmed’ Si CMOS chip: 20 μm Si Pixel resistive layer1 μm SU8 eq. Anode pads1 μm Al Grid1 μm Al Grid resistive layer5 μm SU8 eq. Cathode1 μm Al

Gas instead of Si Pro: - no radiation damage in sensor - modest pixel input circuitry - no bias current, no dark current (in absence of HV breakdowns..!) - requires (almost) only digital CMOS readout chip - low detector material budget Typical: Si foil. New mechanical concepts: self-supporting pressurised co-centric balloons - low power dissipation - (12”) CMOS wafer  Wafer Post Processing  dicing 12” pcs - no bump bonding - ‘simple’ assembly - operates at room temperature - less sensitive for X-ray background - 3D track info per layer Con: - Gas chamber ageing: not known at this stage - Needs gas flow (but can be used for cooling….)

How to proceed? - InGrid 1 available for tests in October: - rate effects (all except change in drift direction) - ageing (start of test)  Proof-of-principle of signal generator: Xmas 2004! - InGrid 2: HV breakdowns, beamtests with MediPix (TimePix1 in 2005) - TimePix2: CMOS chip for Multi Project Wafer test chip GOSSIPO ! Dummy wafer

Essential Ingredients of GOSSIP CMOS chip RATE Assume application in Super LHC: - Bunch crossing 25 ns - 10 tracks per (25 ns cm 2 ) - 10 e- per track (average: Landau fluct.) So: 4 MHz/mm 2 tracks!, 40 MHz/mm2 single electrons!

Charge signal on pixel input pad Q ns - Signal shape is well defined and uniform - No bias current, no dark current - Signal is subject to exponential distribution - may be large, but limited by - chamber ageing - space charge (rate) effects

Input Pad capacity preamp stage, noise, power - Input pads may be small: focusing Too small pads: chamber ageing - capacity to neighbors & metal layers - capacity due to gas gain grid - Pixel size: 50 x x 20 μm 2 4 fF seems feasible

Time resolution preamp-disc speed, noise, power - Measurement 3 rd coordinate: σ drift time : 25/16 = 1.5 ns - Time over threshold: slewing correction - drift time related to BX Record: leading edge - BX trailing edge - BX BX ID

Data Readout ALL data: 80 MB s -1 mm -2 ( 15 GB/s per chip) Maybe possible in 10 years from now: - optical fibre per chip - Vertex can be used as trigger For SLHC: Use BX ID info (typical Vertex policy) - tell BX ID to all (Rows/Columns/Pixels) - get data from (Row/Column/Pixel)

Gossipo MultiProjectWafer submit in 130 nm CMOS technology Test of essential GOSSIP ingredients: - Low power, low input capacity preamp/shaper/discriminator ns TDC (per discriminator output) - Data transfer Maybe not all of this in a first submit Maybe with less ambitious specifications

Amplifier-shaper-discriminator - How to apply a test pulse? - using gas gain grid (all channels fire) - capacitive coupling test pulse strip - reality: with a gas gain grid(!) - What to do with the output? - (bonded) contact: digital feedback?! - TDC + DAQ? TDC ns clock: derived on-board from 40 MHz BX clock? MHz clock distribution (per pixel?!) - DLL?

(My) goal of this meeting: - Are there any showstoppers in this stage? - can we define a Gossipo concept (block diagram)? - Can we estimate the amount of work?